This invention relates to apparatus for illuminating an object and for providing a uniform, thin line of light onto an object for line scan applications. The invention relates to light line units of modular design that can used individually or can be butted end to end to provide very long, seamless linear beams of light. The invention is more particularly directed to an optical fiber based unit which includes an internal light source and where the fibers convert the illumination from that source into a thin, long line of light.
Modular light line units of this general type are discussed in U.S. Pat. No. 5,550,946. In the modular units of that design, there is a bundle of optical fibers that fan out into a single row of fibers, in a manner that allows the units to be placed end to end to create a long line of light. The housings for these light line units are in the form of top and bottom jaws, and these jaws may be formed with triangular teeth to hold the optical fibers in place. In some versions, the jaws may be smooth on one side or on both sides. In addition, an external light source was employed, which required using a light conduit to extend from the light source to the light line module, and typically a separate light source would be needed for each module.
Light line units can be employed in a variety of applications where a long, narrow strip of light is needed. Light line units can be used in line-scan applications, e.g., with line-scan type CCD cameras in web-type applications, i.e., for endless belt inspection or for inspection of carpeting. Fluorescent tubes have been employed behind an elongated aperture to produce a line of light. The fluorescent tube light line units have difficulty producing a line of light that is uniform from one end of the line to the other, or a light that remains uniform over time. The fluorescent units have temperature-sensitive output fluctuations, and outputs that vary with age and with other conditions. Also, if two units are to be joined to provide a light line of extra length, there is additional illumination drop-off between modules.
One type of optical fiber line illuminators is described in U.S. Pat. No. 4,952,022 to Genovese. There, the illuminating device is comprised of a bundle of large-diameter fibers, in which the distal ends or termini are deformed into a rectangular cross section, the idea being production of a linear beam that is uniform along the output of the array. However, that patent does not address how to join two or more units to produce a very long linear beam. In addition, an external light source is required for each unit. Other fiber based systems for transmitting a linear beam of light from a lamp to a workpiece are described in U.S. Pat. No. 3,192,843 to Kapany et al.
In a number of industrial applications, it is necessary to provide a line of illumination up to several meters in length, and with uniformities of better than 90% in a transmission or reflective mode. A typical application can be automated quality inspection of a web type product that travels past, for example a fabric or carpet. The quality of the inspection depends entirely on the uniformity of the light source, that is, on uniformity across the light line. Such high uniformity has been difficult to achieve using standard techniques, such as apertured fluorescent lamps. In addition, inspection of heat-sensitive materials requires remoting the light source from the product, and this has been impossible where conventional linear light sources need to be in proximity to the product.
Replacement of light sources, or of the lamps for the light sources has been a problem as well, as each lamp is expensive and produces significant heat, so it must be situated away from the workpiece being inspected. No one has previously proposed an internal light source for a modular fiber optic light line, nor has anyone proposed a modular lamp replacement that is simple and convenient to adjust or replace.